The invention relates to a flat can to receive a fiber sliver delivered by carders or draw frames. The flat can serves as a container to receive the delivered fiber sliver as well as for its transportation to a spinning mill machine for further processing by means of which the fiber sliver is taken out of the flat can. Flat cans have the advantage over round cans that they can be set up and transported in a more space-saving manner. In addition, more fiber sliver can be stored in a flat can than in a corresponding round can. The problem, by comparison with the round can, is however the filling and the emptying of the flat can, as the quality of the fiber sliver must not be affected in any way.
Known flat cans consist of 2 long, parallel sides and 2 faces. All sides are perpendicular to the bottom of the can (EP 344 484).
The cross-section of the flat can may be rectangular in shape, rectangular with rounded corners (EP 344 484), rectangular with rounded end elements (DE-OS 40 15 938, FIG. 3A) or oval. The can plate which, as is known, is movable and is lowered or raised in function of the fullness of the flat can, also assumes the same form. As is shown in EP 344484, it was customary for flat cans to position the can plate at the level of the can's rim in the empty state. Positioning is achieved by means of springs. The pantograph causes the can plate to always remain horizontal during its up or down movement. However, high jigging speeds nevertheless cause tilting of the can plate.
When the flat can is being filled with fiber sliver it is normally moved back and forth in the longitudinal sense of the can underneath the filling device so that this jigging movement causes the fiber sliver to be deposited on the can plate cycloidically, going from one face of the flat can to the other face. As filling increases, several deposited fiber sliver layers constitute a sliver column which, as a result of its own weight, slowly lowers the can plate to the stop at the can bottom. The can plate has a border which forms an angle down towards the standing surface (can bottom) as is also normally the case with other cans, and reaches as far as the can sides, leaving only a small gap. According to the state of the art (EP 344 484) the can plate is supported at each of its two ends by a helicoidal spring which position the can plate at the upper can rim when it is not burdened.
As soon as the first fiber sliver layer is formed on the can plate, the sliver loop nearest to the front is clearly being displaced in the direction of the can front. This local displacement results from the braking and acceleration forces occurring as the jigging movement reverses. This uncontrolled displacement of the fiber sliver leads to the disadvantage that the sliver loop is pressed over the rim of the can at the front while the first layer is being formed. This displacement increases with the delivery speeds, so that the utilization of flat cans affects the production speed of the carder or of the draw frame. This also applies to the subsequent layers of fiber sliver, even if the displacement is attenuated due to increased adhesive friction between the layers.
This displacement not only affects the quality of the fiber slivers at the front of the can, but the disturbed deposit of the fiber sliver also results in difficulties when the fiber sliver is later withdrawn from the flat can.
The positioning of the can plate according to EP 457 099 (Column 7, lines 41 to 44) even assumes that the can plate should be positioned even slightly higher than the upper can rim, i.e. near the lower rim of the rotary plate of the carder or of the drawing frame. In this manner a required contact pressure is achieved even for the first layers of the fiber sliver. But this has the disadvantage that the can plate of the flat can grinds against the rotary plate immediately at the beginning of the filling action. Wear of the rotary plate surfaces affects the fiber sliver to be deposited.
As the height of the fiber sliver column which consists of a plurality of fiber sliver layers laying on top of each other increases, its mass also increases. In particular as the flat can reaches the reversal points of the jigging movement, this has the effect that due to its mass inertia, the fiber sliver column sways towards the face which is then toward the front. The entire fiber sliver column sways in that case. This swaying is an interference, since it influences the fiber sliver deposit which is still continuing. This not only leads to changes in density of the fiber sliver near the face opposite the depositing positions, but it may also occur that the fiber sliver loops at the front slip into the gap between fiber sliver column and can side due to the swaying of the fiber sliver column and become wedged, an occurrence which increases sliver breakage during subsequent sliver withdrawal. The swaying of the fiber sliver column furthermore produces an undesirable force moment taking effect upon the can side and the can plate.
To counteract this disadvantage, EP 344 484, FIGS. 1 and 2 proposes to install a pantograph (also called a slidable lattice grate or lazy tongs) on the insides of each of the longitudinal side walls to ensure a parallel guidance of the can plate in relation to the sides. However this requires additional design outlay which still is not certain to avoid a tilted position of the can plate when the jigging speeds of the flat can are high.
The pantographs which face each other symmetrically at the longitudinal rims of the can plate cannot prevent a tendency of the can plate of tilting in the direction of its longitudinal axis at high jigging speeds. The danger of jamming against the sides also exists. Tilting of the can plate also has the disadvantage that single, suddenly stressed helicoidal spring, may buckle away from its vertical axis.
The above-mentioned problems have prevented the introduction of the flat can in practical application in the past because the delivery speeds which are normal with the round can could not be achieved.